The present invention relates to a multi-pressure condenser constructed by combining a plurality of shells having different internal pressures.
A condenser used in a nuclear power plant or a thermal power plant has a function of cooling and condensing a turbine exhaust that has been used for an expansion work through a steam turbine to convert it into condensate. The condensate generated in the condenser is fed back to the steam turbine through a feed-water heater and a steam generator. The inside of such a condenser is maintained in a vacuum, and the higher the degree of vacuum, the more the heat consumption rate of the turbine is increased to thereby improve plant efficiency. A typical condenser has a steam turbine at its upper portion and retains the condensate on the bottom side.
The condensate that has been fed from the condenser to the feed-water heater is heated in the feed-water heater by extraction steam from the steam turbine and is then fed to a boiler. At this time, the higher the temperature of the condensate to be fed to the feed-water heater, the more the amount of turbine extraction steam can be reduced, thereby improving plant efficiency.
As an apparatus for increasing the temperature of condensate to be fed to the feed-water heater, there is known a multi-pressure condenser constructed by connecting a plurality of condensers having different internal pressures (Refer to, e.g., Japanese Patent No. 3,706,571, the entire content of which is incorporated herein by reference).
Such a type of condenser will be described in detail with reference to FIG. 5. FIG. 5 is an enlarged vertical cross-sectional view illustrating the outline of a conventional multi-pressure condenser.
A high-pressure stage condenser 101 and a low-pressure stage condenser 103 are connected by a steam duct 110 and a bypass connecting pipe 117. The high-pressure stage condenser 101 has a high-pressure chamber 105 surrounded by a high-pressure shell 102. The low-pressure stage condenser 103 has two chambers defined by a perforated plate 113 provided below a cooling water tube bundle 107 and a low-pressure shell 104: one is a low-pressure chamber 106 defined on the upper side of the perforated plate 113 and the other is a reheat chamber 111 defined on the lower side of the perforated plate 113. Cooling water flowing in the cooling water tube bundle 107 passes through the low-pressure chamber 106 and is introduced into the high-pressure chamber 105. Thus, the temperature of the cooling water is set higher in the low-pressure chamber 106 than in the high-pressure chamber 105, and the pressure of the high-pressure chamber 105 is set higher than that of the low-pressure chamber 106. Further, a tray 115 is provided below the perforated plate 113. Condensate is accumulated in the bottom portions of the high-pressure chamber 105 and the reheat chamber 111.
The steam duct 110 allows the high-pressure chamber 105 and the reheat chamber 111 to communicate with each other, and the bypass connecting pipe 117 guides condensate accumulated in the lower portion of the high-pressure shell 102 to a merger portion 116.
Operational effects of the multi-pressure condenser having such a configuration will be described below.
A turbine exhaust is fed from above the high-pressure stage condenser 101 and the low-pressure stage condenser 103. The turbine exhaust is cooled by the cooling water tube bundle 107 and condensed into condensate.
In the high-pressure stage condenser 101, the condensed condensate is accumulated in the bottom portion of the high-pressure chamber 105. In the low-pressure stage condenser 103, the condensate is accumulated on the perforated plate 113 and dropped to the reheat chamber 111 through holes 114 formed in the perforated plate 113. The perforated plate 113 on which the condensate has been accumulated functions as a pressure barrier between the low-pressure chamber 106 and the reheat chamber 111 to separate the pressure in the low-pressure chamber 106 and the pressure in the reheat chamber 111.
In the reheat chamber 111, the condensate is dropped from the perforated plate 113 to the tray 115 and is further dropped from the end portion of the tray 115 to the bottom portion of the reheat chamber 111. Steam of the high-pressure chamber 105 has been introduced into the gas phase part of the reheat chamber 111 through the steam duct 110. The steam in the high-pressure chamber 105 has a higher pressure than the condensate that has been condensed in the low-pressure chamber 106 and therefore has a high saturation temperature. Thus, it is possible to increase the temperature of the condensate that has been condensed in the low-pressure chamber 106 by reheating the condensate with the steam in the high-pressure chamber 105.
The existence of the tray 115 increases the surface area of the condensate from the phase where the condensate is dropped to the reheat chamber 111 to the place where it is accumulated in the bottom portion of the reheat chamber 111, thereby accelerating heat exchange between the steam and condensate.
The condensate that has been condensed in the high-pressure stage condenser 101 is fed to the merger portion 116 by the bypass connecting pipe 117 and is merged with the condensate of the reheat chamber 111 followed by feeding to a not-illustrated feed-water heater.
According to the multi-pressure condenser having such a configuration, it is possible to obtain the following effects: the temperature of the condensate can be increased; the average value of the turbine exhaust pressure becomes lower than that in a single-pressure type condenser in which all condensers have the same pressure value to increase turbine heat drop; and a difference between the saturation steam temperature of each condenser and the cooling water outlet temperature can be made larger to thereby reduce the condenser cooling area.
As described above, the multi-pressure condenser uses the steam in the high-pressure condenser as a heat source so as to improve plant efficiency. However, in the case where only the steam in the high-pressure condenser is used as a heat source, it is difficult to heat the condensate up to the saturation temperature of the pressure of the high-pressure condenser.